Fabrication of nanoaggregates of a triple hydrophilic block copolymer by cetyltrimethylammonium chloride binding.

A triple hydrophilic block copolymer composed of poly(ethylene oxide), poly(sodium 2-acrylamido-2-methylpropanesulfonate), and poly(methacrylic acid) (PEO-PAMPS-PMAA) does not form a micelle by itself when it is dissolved in water. However, if the anionic PAMPS and/or PMAA blocks are electrically neutralized with a cationic surfactant, such as cetyltrimethylammonium chloride (CTAC), micelle-like nanoaggregates are obtained, where the core is formed by the insolubilized PAMPS and/or PMAA blocks. Formation of the nanoaggregates was confirmed by dynamic light scattering (DLS) measurements and scanning electron microscopy (SEM), while the binding of CTAC to PEO-PAMPS-PMAA was monitored by electrophoresis measurements. The aggregates were characterized by fluorescence spectroscopy as well as DLS and SEM. It was found that the nanoaggregates have a spherical structure, and the hydrodynamic diameter ranges from 125 to 193 nm depending on the concentrations of the PEO-PAMPS-PMAA and CTAC. The critical aggregate concentration is on the order of 10-4 g L-1 when the ionic blocks of PEO-PAMPS-PMAA are fully neutralized with CTAC.